His right arm constantly falls off at the bicep...
Detach the troubled arm from the shoulder socket completely. The problem might be it’s not lining up to the hole of the bicep swivel. From there try to push the bicep
Arm joint all the way in until you hear the crunch or snap. Test it out, good, then snap the shoulder back to the socket
If this is a knockoff, I can’t guarantee anything however, because the parts are cheap on a knockoff
You might need to heat the joints up before you remove